Date : Sun, 21 Mar 2010 16:36:46 +0000
From : adsb@... (Andrew Benham)
Subject: [OT] ADSL capabilities
Darren Grant wrote:
> Every telephone device that is connected to an ADSL enabled line must
have a filter in place. The extra ring signal generated by the master socket
is therefore not used as the ring signal is not passed through a microfilter.
Every microfilter connects to the line with only 2 wires and then contains
its own ring capacitor, to generate a clean ring signal for the phone.
And in so doing breaks the original purpose of the ring wire :-(
When the 'new' phone socket was introduced, pulse dialling
was just about the standard. Installations with multiple
phones were prone to 'bell tinkle' - when one phone dialled out,
other phones on the line would tinkle their bells in cadence
with the dial pulses.
The 'new' phone socket system cures this with the ring wire.
The master socket provides the ring wire to all other sockets.
Every phone connects its ringer between the ring wire and the
'A' wire (one half of the main pair).
The key part of the design is that when off-hook, a phone
connects the ring wire directly to the 'A' wire, shorting out
the ringers of all phones on the line - thus bell tinkle is
impossible as all the ringers are shorted out.
[ Testing that instruments correctly did this was part of the BABT
approval (and the 'Green Circle' sticker). But it appears that
this has all been thrown out of the window and you can put anything
on your line. ]
When ADSL is installed on a line which has multiple phones including a
pulse-dialling phone on it, bell tinkle is going to reappear if
you go down the 'every phone shall have a microfilter' route. The
only clean solution, as Darren mentioned, is a filtered faceplate
for the incoming line at the NTE5 master socket. This separates
the ADSL and phone signals early in the layout, and then the existing
3-wire phone wiring can work as designed.
--
Andrew Benham adsb@...
Southgate, London N14, United Kingdom
The gates in my computer are AND OR and NOT, not "Bill"